Open /etc/rc.conf once more and scroll down to the network config section. Here is where you define how your network cards should obtain their IP. The LAN card will have a static IP, I am going with 10.0.0.1 because it is easy to type. I am building a gateway for a small student home with 4 rooms so I am keeping the subnet fairly small: 4 bits allow 16 IP's.

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Now you'll need to configure the network interfaces. The best way to so do is using [[netcfg]] profiles, instead of the regular [[network]] daemon. You'll need to create two profiles.

−

16 - 3 IP's:

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* /etc/network.d/extern0-profile

−

* one for the network address: 10.0.0.0

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CONNECTION='ethernet'

−

* the gateway: 10.0.0.1

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DESCRIPTION='Public Interface.'

−

* and the broadcast address: 10.0.0.15 leaves 13 IP's for computers on the LAN. This translates into:

{{Note|The new interface method does not work with this because it only supports single interfaces for the time being. However, the old method is still supported, and should still be used as shown.}}

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* /etc/network.d/intern0-profile

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CONNECTION='ethernet'

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DESCRIPTION='Private Interface.'

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INTERFACE='intern0'

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IP='static'

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ADDR='10.0.0.1'

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NETMASK='255.255.255.0'

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BROADCAST='10.0.0.255'

+

+

{{Note|The example configuration above assumes a full subnet. If you are building the gateway for a small amount of people, you will want to change the netmask and broadcast to accommodate a smaller range.}}

+

+

Next up is to set up the interfaces in /etc/rc.conf.

+

+

* Define the profiles

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NETWORKS=(extern0-profile intern0-profile)

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* Replace the "network" daemon with the netcfg one: "net-profiles"

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DAEMONS=( ... net-profiles ... )

==ADSL connection==

==ADSL connection==

Revision as of 00:46, 18 September 2011

This template has only maintenance purposes. For linking to local translations please use interlanguage links, see Help:i18n#Interlanguage links.

This article is a tutorial for turning a computer into an internet gateway/router. It focuses on security, since the gateway is connected directly to the Internet. It should not run any services available to the outside world. Towards the LAN, it should only run gateway specific services. It should not run httpd, ftpd, samba, nfsd, etc. as those belong on a server in the LAN as they introduce security flaws.

This article does not attempt to show how to set up a shared connection between 2 PCs using cross-over cables. For a simple internet sharing solution, see Internet Share.

Hardware Requirements

At least 1 GB of hard drive space. The base install will take up around 500MB of space and if you want to use a caching web proxy, you will need to reserve space for the cache as well.

At least two physical network interfaces: a gateway connects two networks with each other. You will need to be able to connect those networks to the same physical computer. One interface must connect to the external network, while the other connects to the internal network.

A hub, switch or UTP cable: You need a way to connect the other computers to the gateway

Conventions

Conventions in this guide will be to use non-realistic interface names, to avoid confusion about which interface is which.

intern0: the network card connected to the LAN. On an actual computer it will probably have the name eth0, eth1, etc.

extern1: the network card connected to the external network (or WAN). It will probably have the name eth0, eth1, etc.

Installation

A fresh install of Arch Linux is the easiest to start from, as no configuration changes have been made and there is a minimal amount of packages installed. This is helpful when attempting to reduce security risk.

Partitioning

For security purposes, /var, /tmp and /home should be separate from the / partition. This prevents disk space from being completely used up by log files, daemons or the unprivileged user. It also allows different mount options for those partitions. If you have already partitioned your drive, the gparted livecd can be used to resize, move, or create new partitions.

Your home and root partitions can be much smaller than a regular install since this is not a desktop machine. /var should be the largest partition - it is where databases, logs and long-term caches are stored. If you have a lot of RAM, mounting /tmp as tmpfs is a good idea, so making a disk partition for it during the initial install is unnecessary.

Post-Installation

After installation boot Arch and upgrade all the packages to their latest version:

Note: The example configuration above assumes a full subnet. If you are building the gateway for a small amount of people, you will want to change the netmask and broadcast to accommodate a smaller range.

Next up is to set up the interfaces in /etc/rc.conf.

Define the profiles

NETWORKS=(extern0-profile intern0-profile)

Replace the "network" daemon with the netcfg one: "net-profiles"

DAEMONS=( ... net-profiles ... )

ADSL connection

Using rp-pppoe, we can connect an ADSL modem to the extern1 of the firewall and have Arch manage the connection. Make sure you put the modem in bridged mode though, otherwise the modem will act as a router too.

# pacman -S rp-pppoe

Configuration: rp-pppoe

/usr/sbin/pppoe-setup

The questions are all documented. You can select "no firewall" because we will let Shorewall / iptables handle that part.

DNS and DHCP

We will use dnsmasq, a DNS and DHCP daemon for the LAN. It was specifically designed for small sites.

First, install dnsmasq:

# pacman -S dnsmasq

Now, dnsmasq needs to be configured. To do this:

Edit /etc/dnsmasq.conf and add the following lines

interface=intern1 # make dnsmasq listen for requests only on intern1 (our LAN)
expand-hosts # add a domain to simple hostnames in /etc/hosts
domain=foo.bar # allow fully qualified domain names for DHCP hosts (needed when
# "expand-hosts" is used)
dhcp-range=10.0.0.2,10.0.0.14,255.255.255.240,1h # defines a DHCP-range for the LAN:
# from 10.0.0.2 to .14 with a subnet mask of 255.255.255.240 and a
# DHCP lease of 1 hour (change to your own preferences)

Somewhere below, you will notice you can also add "static" DHCP leases, i.e. assign an IP-address to the MAC-address of a computer on the LAN. This way, whenever the computer requests a new lease, it will get the same IP. That is very useful for network servers with a DNS record. You can also deny certain MAC's from getting an IP. Evil!! ^_^
Now start dnsmasq

Connection sharing

iptables

Shorewall

Shorewall, an iptables frontend, can be used as an easier alternative.

# pacman -S shorewall

Shorewall configuration

Time to configure Shorewall! Open its config file in /etc/shorewall/shorewall.conf and start editing. The file is very well documented.

SUBSYSLOCK=/var/run
IP_FORWARDING=On : it is a gateway, remember! ;)
STARTUP_ENABLED=Yes # when you are done editing

After installing shorewall, run

$ pacman -Ql shorewall | grep Sample

to see where the sample files are. cd into the directory "two-interfaces" and copy the contents to the /etc/shorewall/ directory.
Now use Shorewall's guide to set up the files correctly.

Read the document carefully. Take special care to change eth0 and eth1 (or ppp0 in if you are using PPPoE where appropriate in your config files as the Shorewall guide uses different names for the interfaces. When you have followed it thoroughly, make the following changes:

/etc/shorewall/interfaces : add "dhcp" to the loc line to allow computers on the LAN to make use of our DHCP server

/etc/shorewall/rules : add

ACCEPT loc $FW TCP 2367

but change 2367 into whatever port you have your SSH server listening on.

Finally, run

# /etc/rc.d/shorewall start

From here on, the Arch box is operational. Connect a hub or switch to intern0 and a computer to the LAN to test it.

Port forwarding (DNAT)

/etc/shorewall/rules : here is an example for a webserver on our LAN with IP 10.0.0.85. You can reach it on port 5000 of our "external" IP.

DNAT net loc:10.0.0.85:80 tcp 5000

Cleanup

Now that the installation has been performed, it is necessary to remove as many packages as possible. Since we are making a gateway, keeping unneeded packages only "bloats" the system, and increases the number of security risks.

First, check for obsolete/deprecated packages (likely after a fresh install and massive series of updates):

$ pacman -Qm

Review the list of explicitly installed packages that are not dependencies and remove any that are unneeded. Having only needed packages installed is an important security consideration.

$ pacman -Qet

Completely remove the packages you do not need along with their configuration files and dependencies:

# pacman -Rsn package1 package2 package3

Logrotate

You should review the logrotate configuration to make sure the box is not brought down by lack of diskspace due to logging.

Logrotate is installed by default, so you will not have to install it.

Optional additions

Remote administration

OpenSSH can be used to administer your router remotely. This is useful for running it "headless" (no monitor or input devices).

Caching web proxy

See Squid or Polipo for the setup of a web proxy to speed up browsing and/or adding an extra layer of security.

Time server

Then, configure shorewall or iptables to allow NTP traffic in and out.

Content filtering

Install and configure DansGuardian if you need a content filtering solution.

Traffic shaping

Traffic shaping is very useful, especially when you are not the only one on the LAN. The idea is to assign a priority to different types of traffic. Interactive traffic (ssh, online gaming) probably needs the highest priority, while P2P traffic can do with the lowest. Then there is everything in between.